packrat::restore() fails for Github package in Dockerfile

This line runs fine inside the Dockerfile:

devtools::install_github('nik01010/dashboardthemes', lib = '/root/shiny-planting-schedule/packrat/lib')

But if I try to packrat::restore() inside the Dockerfile I get an error when installing the above package from Github:

packrat::restore(project = '/root/shiny-planting-schedule')

Error:

Installing scales (1.0.0) ...
        OK (built source)
Installing dashboardthemes (1.0.5) ...
FAILED
Error in getSourceForPkgRecord(pkgRecord, srcDir(project), availablePackagesSource(repos = repos),  :
  Failed to download package from URL:
- 'https://api.github.com/repos/nik01010/dashboardthemes/tarball/91524951f8ac635c46711b7693bd468751ffb995'
Calls: <Anonymous> ... restoreImpl -> playActions -> installPkg -> getSourceForPkgRecord
Execution halted
The command '/bin/sh -c R -e "packrat::restore(project = '/root/shiny-planting-schedule')"' returned a non-zero code: 1

Here is the full Dockerfile:

# Install R version 3.6.1 with rstudio, tidyverse, and tex/publishing related packages
FROM rocker/verse:3.6.1

# Install Ubuntu packages
RUN apt-get update && apt-get install -y \
  sudo \
  gdebi-core \
  pandoc \
  pandoc-citeproc \
  libcurl4-gnutls-dev \
  libxml2-dev \
  libudunits2-dev \
  libcairo2-dev \
  libgdal-dev \
  libgeos-dev \
  libproj-dev \
  libxt-dev \
  libssl-dev

RUN mkdir /root/shiny-planting-schedule
RUN mkdir /root/shiny-planting-schedule/app
RUN mkdir /root/shiny-planting-schedule/packrat
RUN mkdir /root/shiny-planting-schedule/packrat/lib

COPY packrat /root/shiny-planting-schedule/packrat

RUN install2.r devtools \
  && rm -rf /tmp/downloaded_packages/ /tmp/*.rds

RUN R -e "devtools::install_github('rstudio/packrat')"

COPY packrat /root/shiny-planting-schedule/packrat

# Restore project packages with packrat
RUN R -e "packrat::restore(project = '/root/shiny-planting-schedule')"

# Copy app folder to image
COPY app /root/shiny-planting-schedule/app

# Make the ShinyApp available at port
EXPOSE 3838

CMD ["R", "-e", "setwd('root/shiny-planting-schedule'); source('/root/shiny-planting-schedule/app/source-file.R')"]

Reproduce the failure from the Dockerfile, comparing the successful devtools::install_github call with packrat::restore(project = '/root/shiny-planting-schedule'). Trace the restore path around the failed GitHub tarball URL; done means dashboardthemes installs successfully during the Docker build and the restore command exits successfully.